Field of the Invention
The present application relates to an assembly for packaging and dispensing a product under pressure, and in particular a cosmetic product. The invention is most particularly adapted for the packaging and dispensing under pressure, certain hair-care products, Such as dye products, and particularly tone-on-tone dye.
There are in existence so-called "tone-on-tone" oxidation dyes which are packaged in cans containing an aluminum pouch delimiting two volumes which are separate from each other. The pouch includes a first volume communicating with a dispensing head and containing the dye, and a second volume containing a propellent gas, particularly butane 3.2. Products of this type are very sensitive to light and oxygen. At the time of use, the dye is mixed with an oxidizing cream packaged in a separate can. Apart from the lack of reliability, packaging of this type is extremely expensive.
With a view to producing a more economical assembly, there have been developed piston-type cans, or cans with another separation means, comprising a can surmounted by a value and by a dispensing head. In these types of containers, the product is pressurized by means of a propellent gas kept separate from the product by the movement of a piston sliding in the can in substantially a leaktight manner, or by other movable separation barrier means. In the case of the piston can, the seal is conventionally provided by an O-ring arranged at the periphery of the piston and by a scraper lip bearing tightly against the inner walls of the can. Despite all these precautions to ensure the piston has a good seal, this seal has not proved to be satisfactory. Indeed, as the can is extruded, its inner face presents longitudinal microgrooves which are sufficient to allow a slow diffusion of the propellent gas into the other compartment containing the product. Thus, over time, and through the action of the gaseous pressure and osmotic pressure, the propellent butane diffuses along the piston and dissolves in the formula, until the pressures are equalized.
When the user wishes to use the contents of the can, restoring the product to atmospheric pressure gives rise to a bubbling-up of the dissolved gases and "foaming" of the formula, which is very badly perceived by consumers who may be led to believe that the product is defective.
EP-A-0,642,839 describes a device for dispensing and packaging a fluid product contained in a pressurized container with the aid of a propellent gas contained in a compartment of the container, separate from the product to be dispensed via a piston. The container is surmounted by a manually actuated valve. Between two uses, the compartment containing the propellent gas is emptied of gas by means of a microslot so that, after a certain period of time, the compartment is at atmospheric pressure. According to that document, opening and closing of the valve for dispensing the product are brought about by means of an actuating mechanism in the form of a push-button controlled independently of the pressure inside the compartment containing the propellent gas. A design of this type increases the amount of handling needed at the time of use.
Therefore, one of the objects of the invention is to propose an assembly for packaging and dispensing a product of the type referred to above which does not have the drawbacks discussed in the aforesaid with regard to conventional devices.
A particular object of the invention is to provide a reliable, economical assembly which keeps the product completely separate from the propellent gas throughout the product's life.
Further objects of the invention will become apparent in a detailed manner from the following description.